Was that because Berkshire would have to pay taxes on them?

No, it wasn't a tax issue. Had you listened closely, you would have understood that it was absurd to report unrealized gains and losses in GAAP because it is so volatile. What if the last day of the quarter happens to have seen a broad 5% decline in markets, only to see the 5% recovered in the first week of the next quarter? It's absurd to have GAAP move rapidly up and down due to market vagaries. It makes GAAP mostly useless for such companies.

and he just hated giving a more accurate picture to the shareholders?

And this is just plain ridiculous. Berkshire has always given an accurate accounting of the value of all holdings regardless of what is required to be accounted for in GAAP. In their annual letters, over all the decades they've existed, they literally compare their value to common benchmarks.